1. Technical Field
The present invention relates to a battery pack manager.
2. Background Art
A battery pack comprised of nickel-metal hydride batteries has hitherto been used as a power source for a motor in a motor vehicle, like a hybrid electric vehicle and a pure electric vehicle, or as a drive source for a load. A lithium ion battery exhibits higher energy density than that exhibited by other secondary batteries and is also superior to the other secondary batteries in terms of charging and discharging efficiency. For these reasons, substitution of nickel-metal hydride batteries for lithium ion batteries is under consideration.
A battery pack built in a motor vehicle is made by connecting a plurality of blocks in series, and each of the blocks is further made by connecting a plurality of battery cells in series. In order to control a state of the battery pack or detect an anomaly in the battery pack, a manager is provided on a per-block basis, thereby detecting voltages of the battery cells.
A disclosure of JP 2006-29895 A is series-connected or so-called stacked use of a required number of integrated circuits for use in monitoring a battery voltage. Specifically, a first integrated circuit and a second integrated circuit are provided for series-connected eight battery cells. Provided that the first integrated circuit is a high level integrated circuit and that the second integrated circuit is a low level integrated circuit, each of the high level integrated circuit and the low level integrated circuit has, as power terminals, a VDD terminal that is a terminal of the highest electric potential VDD and a VSS terminal that is a terminal of the lowest electric potential VSS. The VSS terminal of the high level integrated circuit and the VDD terminal of the low level integrated circuit are commonly connected together. By way of a resistive potential dividing circuit, a signal output terminal SOUT of the high level integrated circuit and a reference voltage terminal REFU of the low level integrated circuit are connected together between the high level integrated circuit and the low level integrated circuit. A divided potential output terminal of the resistive potential dividing circuit is connected to a signal input terminal SIN of the low level integrated circuit. The configuration makes it possible to transmit details of a cell anomaly detected by the high level integrated circuit to a controller by way of the low level integrated circuit.
A disclosure of JP 2007-282413 A includes taking a voltage across both ends of the battery cells of any block in the battery pack into a flying capacitor by means of selective activation of a switching element and further into a microcomputer; managing a state of the battery cells by a management unit provided on a per-block basis; and discharging the battery cells by the respective management units.
Incidentally, the management unit (an integrated circuit) that detects a voltage of each of the blocks making up the battery pack operates upon receipt of a power supply from a secondary battery that is an object of management. Because of variations in electric power consumed by the plurality of management units, variations often arise in a state of charge (SOC) of the blocks making up the battery pack.